Magnetic core-shell microspheres were developed to extract rare earth elements (REEs) from aqueous and brine solutions with up to 99.99% removal efficiency. The shell, composed of a thermally and chemically stable functionalized metal-organic framework (MOF), is grown over a synthesized Fe3O4 magnetic core (magnetite@MOF). The composite particles can be removed from the mixture under an applied magnetic field, offering a practical, and efficient REE-removal process.

Rare-earth elements (REEs) have significant commercial and military uses.1-3 However, REE extraction through conventional mining processes is expensive and feasible at only a few locations worldwide. Alternative methods are needed to produce REEs from more geographically disperse resources and in a cost effective, environmental friendly manner.4,5 Among various sources, geothermal brine, used for generating geothermal energy can possess attractive concentrations (ppb to ppm level) of REEs along with other dissolved metal ions.6 A system that can selectively trap the REEs using an existing geothermal power plant infrastructure would be an attractive additional revenue stream for the plant operator that couldmore » accelerate the development and deployment of geothermal plants in the United States and rest of the world.7,8 Here, we demonstrate a magnetic core-shell approach that can effectively extract REEs in their ionic form from aqueous solution with up to 99.99% removal efficiency. The shell, composed of thermally and chemically stable functionalized metal-organic framework (MOF), is grown over a synthesized Fe3O4 magnetic core. Magnetic susceptibility of the particles was found to decline significantly after in situ growth of a MOF shell, which resulted from oxidation of Fe2+ species of the magnetite (Fe3O4) to Fe3+ species (maghemite). The core-shell particles can be completely removed from the mixture under an applied magnetic field, offering a practical, economic, and efficient REE-removal process.« less

Rare earth metals are critical materials in a wide variety of applications in generating and storing renewable energy and in designing more energy efficient devices. Extracting rare earth metals from geothermal brines is a very challenging problem due to the low concentrations of these elements and engineering challenges with traditional chemical separations methods involving packed sorbent beds or membranes that would impede large volumetric flow rates of geothermal fluids transitioning through the plant. We are demonstrating a simple and highly cost-effective nanofluid-based method for extracting rare earth metals from geothermal brines. Core-shell composite nanoparticles are produced that contain a magneticmore » iron oxide core surrounded by a shell made of silica or metal-organic framework (MOF) sorbent functionalized with chelating ligands selective for the rare earth elements. By introducing the nanoparticles at low concentration (≈0.05 wt%) into the geothermal brine after it passes through the plant heat exchanger, the brine is exposed to a very high concentration of chelating sites on the nanoparticles without need to pass through a large and costly traditional packed bed or membrane system where pressure drop and parasitic pumping power losses are significant issues. Instead, after a short residence time flowing with the brine, the particles are effectively separated out with an electromagnet and standard extraction methods are then applied to strip the rare earth metals from the nanoparticles, which are then recycled back to the geothermal plant. Recovery efficiency for the rare earths at ppm level has now been measured for both silica and MOF sorbents functionalized with a variety of chelating ligands. A detailed preliminary techno-economic performance analysis of extraction systems using both sorbents showed potential to generate a promising internal rate of return (IRR) up to 20%.« less

Rare earth elements (REEs) are critical to our modern world. Recycling REEs from used products could help with potential supply issues. Extracting REEs from chloride media with tetrabutyl diglycolamide (TBDGA) in carbon dioxide could help recycle REEs with less waste than traditional solvents. Carbon dioxide as a solvent is inexpensive, inert, and reusable. Conditions for extraction of Eu from aqueous chloride media were optimized by varying moles percent of 1-octanol modifier, temperature, pressure, Eu concentration, TBDGA concentration, Cl– concentration, and HCl concentration. These optimized conditions were tested on a Y, Ce, Eu, Tb simulant material, REEs containing NdFeB magnets, andmore » lighting phosphor material. The optimized conditions were found to be 23 °C, 24.1 MPa, 0.5 mol% 1-octanol, with an excess of TBDGA. At these conditions 95 ± 2% Eu was extracted from 8 M (mol/m3) HCl. Extraction from the mixed REE simulate material resulted in separation of Y, Eu, and Tb from the Ce which remained in the aqueous solution. The extraction on NdFeB magnet dissolved into 8 M HCl resulted in extraction of Pr, Nd, Dy, and Fe >97%. This ends in a separation from B, Al, and Ni. Extraction from a trichromatic lighting phosphor leachate resulted in extraction of Y and Eu >93% and no extraction of Ba, Mg, and Al.« less

The overall goal of this SBIR Phase I project was to demonstrate the feasibility of an ionic liquid (IL) process for the direct extraction of rare earth elements (REEs) from coal and demonstrate the recovery of REEs from the coal-IL solution, in a sustainable and energy efficient manner. Phase I confirmed the feasibility of this approach on both coal and coal by-products, resulting in 92-100% extraction of REEs from coal into IL, resin separation, and recovery of REE solids via developed electrochemical methods. In this Phase I project, we demonstrated the technology and evaluated IL design, REE extraction parameters, andmore » REE recovery methods, which have provided essential chemistry and engineering knowledge needed for our process design and scale-up to a mini-pilot prototype system in Phase II. Below are important Phase I accomplishments: Ionic liquid design. We have successfully demonstrated the extraction of REEs from coal and fly ash into specifically designed ILs in a simple and energy efficient manner. REE extraction and recovery from coal was performed via direct treatment of coal with intelligently designed task-specific ILs. The IL chosen for these processes possesses an ideal combination of excellent solvation ability, nonvolatility, low toxicity, proven recyclability, and availability at the multi-ton scale. Rare earth element extraction. Detailed studies were performed to determine variables which affect dissolution parameters and REE extraction efficiency in order to determine optimal treatment parameters. Parameters which affect dissolution were determined, and an optimal treatment process was developed. We can reproducibly extract 92-100% of REEs from coal into IL in as little as two minutes of treatment. Preliminary studies indicate that our process can also be applied to other sources of coal and ash from different U.S. mines. Rare earth element recovery. REE separation from coal-IL solutions was demonstrated using both commercially available resins and chitin-based sorbents. The resins tested were able to efficiently extract 99% of REEs from solutions of coal-IL and fly ash-IL. It was demonstrated that the REEs could be recovered from the resins into aqueous solutions. An electrochemical method for the recovery of REEs directly from the aqueous eluents from these separation processes has been demonstrated. Major products of this process are the production of individual and mixed REEs. Additional applications include the valorization of co-products from recovered REE-free residues, oil, and solid precipitate. Co-products include valuable metals (e.g., Li, V), carbon materials, and chemicals which will increase the commercialization value of this process. Secondary applications include the use of this process in coal by-product remediation/processing, as this process has been demonstrated with fly ash. We are now ready to scale-up our processes in Phase II from the current 10 mL benchtop scale to a 3 L mini-pilot demonstration unit in order to fine tune the engineering parameters necessary to further design and develop, also during Phase II, a prototype pilot unit (20 L) for a continuous processing system.« less